1. Technical Field of the Invention
The present invention relates to a cosmetic regime or regimen for promoting pigmentation of the skin and/or skin appendages, in particular of the hair and/or of body hair, and to the formulation of 15-hydroxyprostaglandin dehydrogenase inhibitors into compositions suited to combat canities. This invention relates in particular to the administration of tetrazole, styrylpyrazole, phenylfuran, phenylthiophene, phenylpyrrazole, pyrazolecarboxamide, 2-thioacetamide or azo compounds as agents for promoting pigmentation of the skin and/or skin appendages, and/or for limiting and/or preventing depigmentation.
2. Description of Background and/or Related and/or Prior Art
The color of the hair and of the human skin depends on various factors, and in particular on the seasons of the year, on race, on sex and on age. It is mainly determined by the concentration of melanin produced by melanocytes. Melanocytes are specialized cells that, by means of specific organelles, melanosomes, synthesize melanin.
Melanin synthesis, or melanogenesis, is complex and involves, diagrammatically, the following main steps:    Tyrosine→Dopa→Dopaquinone→Dopachrome→Melanin
Tyrosinase (monophenol dihydroxyl phenylalanine: oxygen oxidoreductase EC 1.14.18.1) intervenes in this series of reactions by catalyzing in particular the reaction consisting of the conversion of tyrosine to Dopa (dihydroxyphenylalanine) and the reaction consisting of the conversion of Dopa to Dopaquinone.
The upper part of the hair follicle is like a tubular invagination of the epidermis that extends to the deep layers of the dermis. The lower part, or hair bulb, itself comprises an invagination in which is found the dermal papilla. Around the dermal papilla, in the lower part of the bulb, is a zone populated with highly proliferative cells (cells of the matrix). These cells are the precursors of the keratinized cells that will constitute the hair. The cells that result from the proliferation of these precursors migrate vertically into the bulb and gradually become keratinized in the upper part of the bulb, and this group of keratinized cells will form the hair shaft. The pigmentation of the hair and of the body hairs requires the presence of melanocytes in the bulb of the hair follicle. These melanocytes are in an active state, i.e., they synthesize melanins. These pigments are transmitted to the keratinocytes intended to form the hair shaft, which will result in the growth of a pigmented hair or body hair. This structure is called “follicle pigmentary unit”.
It is known that, in most populations, brown coloration of the skin and the maintaining of a constant color of the hair are considerable aspirations.
It is accepted that the appearance of gray or white body hairs and/or hair, or canities, is associated with a decrease in melanin in the hair shaft. This phenomenon occurs naturally during the life of an individual. However, human beings seek to have a younger appearance and, for esthetic purposes, they often attempt to combat this phenomenon, especially when it occurs at a relatively early age.
Many solutions have thus been proposed in the field of artificial coloration through the introduction of exogenous dyes aimed at giving the hair a color that is as close as possible to its natural color. Another approach consists in stimulating the natural pigmentation pathway.
Among the solutions proposed, mention may be made of compositions containing a phosphodiesterase inhibitor (WO 95/17161), DNA fragments (WO 95/01773), diacyl glyerol (WO 94/04122), prostaglandins (WO 95/11003) or pyrimidine 3-oxide derivatives (EP 829260).
However, need continues to exist for novel solutions that are effective for promoting pigmentation of the skin, of the hair and/or of body hair, and therefore preventing or decreasing canities.